510
FXUS66 KPQR 151037
AFDPQR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND OR
337 AM PDT MON SEP 15 2025
SYNOPSIS
SHOWERS ASSOCIATED WITH SUNDAYS FRONTAL PASSAGE HAVE
DIMINISHED, LEAVING DRY AND CALMER CONDITIONS FOR TODAY.
OFFSHORE FLOW WILL STRENGTHEN TONIGHT INTO TUESDAY, PRODUCING
WARM TEMPERATURES AND BREEZY TO LOCALLY STRONG EASTERLY WINDS
THROUGH THE COLUMBIA RIVER GORGE AND CASCADE GAPS. ONSHORE FLOW
AND A WEAK FRONT BRUSH THE COAST MIDWEEK WITH ONLY LIMITED
PRECIPITATION POTENTIAL. A BROADER TROUGHING PATTERN FROM THE
NORTHEAST PACIFIC MAY THEN BRING INCREASING RAIN CHANCES INTO
THE WEEKEND.
SHORT TERM...NOW THROUGH TUESDAY NIGHT
AS OF 4 AM, SKIES
REMAIN MOSTLY CLEAR ACROSS INTERIOR VALLEYS WITH ONLY PATCHY
STRATUS NOTED OVER THE CASCADES. FOG HAS NOT BEEN OBSERVED SO
FAR, THOUGH PATCHY DEVELOPMENT IS STILL POSSIBLE NEAR SUNRISE IN
MORE SHELTERED VALLEYS OF SOUTHWEST WASHINGTON. CONFIDENCE IN
WIDESPREAD DENSE FOG REMAINS LOW.
BUILDING SHORTWAVE RIDGING TODAY ENSURES DRY CONDITIONS WITH
NEAR-SEASONAL HIGHS - MID TO UPPER 70S INLAND AND MID 60S AT THE
COAST. BY THIS EVENING, A THERMALLY INDUCED SURFACE TROUGH
STRENGTHENS ALONG THE COAST, TIGHTENING THE OFFSHORE PRESSURE
GRADIENT (-4 TO -6 MB KTTD-KDLS). THIS SETS UP BREEZY TO LOCALLY
STRONG EASTERLIES BEGINNING TONIGHT.
WINDS WILL PEAK LATE TONIGHT INTO TUESDAY MORNING, STRONGEST
THROUGH THE WESTERN COLUMBIA GORGE AND CASCADE GAPS WHERE GUSTS
OF 25-40 MPH ARE EXPECTED. THERE IS A 40-60% CHANCE FOR GUSTS
EXCEEDING 40 MPH IN FAVORED LOCATIONS SUCH AS CROWN POINT AND
THREE CORNER ROCK. WINDS WILL GRADUALLY EASE TUESDAY EVENING AS
GRADIENTS RELAX, WITH GUSTS GENERALLY DROPPING BELOW 20 MPH
OUTSIDE OF EXPOSED TERRAIN.
TEMPERATURES CLIMB SHARPLY TUESDAY UNDER DOWNSLOPE OFFSHORE FLOW
AND COMPRESSIONAL WARMING. INTERIOR VALLEYS CARRY A 70-90%
CHANCE OF REACHING OR EXCEEDING 85 DEGREES, WITH A 10-30% CHANCE
OF TOUCHING 90 DEGREES. A FEW ISOLATED SITES ARE LIKELY TO REACH
90 DEGREES. ELEVATED FIRE WEATHER CONDITIONS WILL ACCOMPANY THE
WARM, DRY, AND BREEZY PATTERN, THROUGH THE STRONGEST WINDS
SHOULD PRECEDE THE LOWEST DAYTIME HUMIDITIES, REDUCING OVERLAP
OF CRITICAL THRESHOLDS.
LONG TERM...WEDNESDAY THROUGH SUNDAY
ONSHORE FLOW RETURNS
WEDNESDAY AS A WEAK TROUGH BRUSHES THE REGION. LIGHT RAIN
(10-20% CHANCE) WILL BE CONFINED TO THE IMMEDIATE COAST AND
ADJACENT WATERS, WHILE INLAND AREAS ARE EXPECTED TO REMAIN DRY.
BEYOND MIDWEEK, ENSEMBLE GUIDANCE DIVERGES ON THE AMPLITUDE AND
TIMING OF SUBSEQUENT TROUGHING. ROUGHLY 80% OF MEMBERS FAVOR
DRIER WEATHER THURSDAY INTO FRIDAY, WHILE 20% MAINTAIN LIGHT
SHOWERS ALONG THE COAST TIED TO CONTINUED WEAK TROUGHING.
ATTENTION THEN TURNS TO THE WEEKEND, WHEN MORE ORGANIZED
TROUGHING FROM THE NORTHEAST PACIFIC DIGS INTO THE REGION. THIS
FEATURE MAY REINTRODUCE PRECIPITATION CHANCES AREA-WIDE, WITH
CURRENT ENSEMBLE PROBABILITIES SHOWING A 20-40% CHANCE FOR
MEASURABLE RAINFALL ACROSS SOUTHWEST WASHINGTON AND NORTHWEST
OREGON LATE SATURDAY INTO SUNDAY. CONFIDENCE IS MODEST AT THIS
RANGE, BUT TRENDS SUPPORT INCREASING RAIN CHANCES OVER THE
WEEKEND COMPARED TO THE MIDWEEK SYSTEM. TEMPERATURES COOL
ACCORDINGLY, WITH ENSEMBLE RANGES GENERALLY MID 70S TO LOW 80S
SATURDAY, THEN LOW TO UPPER 70S BY SUNDAY. ~HALL
AVIATION
PREDOMINATELY VFR CONDITIONS WITH MOSTLY CLEAR SKIES.
THE CLEAR SKIES UNDER BUILDING HIGH PRESSURE FOLLOWING
YESTERDAY'S RAIN COULD LEAD TO FOG OR LOW STRATUS DEVELOPMENT IN
THE WILLAMETTE VALLEY BETWEEN 10-18Z MONDAY. THERE'S AROUND A
35-50% CHANCE OF IFR CEILINGS ALONG THE I-5 CORRIDOR IN THE
WILLAMETTE VALLEY WITH BEST CHANCES ARE FOR THE PORTLAND AREA
TERMINALS WHERE WINDS WILL BE WEAKEST. CONDITIONS MAY FLUCTUATE
BETWEEN MVFR AND IFR THROUGH THIS TIME PERIOD. THERE IS HIGH
PROBABILITY FOR FOG FORMATION FOR COAST RANGE AND CASCADE VALLEYS.
ALONG THE COAST, EASTERLY WINDS WILL PREVENT MARINE STRATUS FROM
FORMING, THOUGH THEY COULD PUSH SOME STRATUS FROM THE COAST RANGE
EAST TO COASTAL TERMINALS. HOWEVER, WINDS ALONG THE FAR NORTHERN
OREGON COAST WILL BE MORE NORTHERLY AND LIGHTER, WHICH WILL
BETTER ALLOW FOR STRATUS FORMATION WITH A 50-70% CHANCE OF IFR
CONDITIONS AT KAST BETWEEN 10-18Z MON. WINDS INLAND ARE MORE
NORTHERLY AND LIGHT, INCREASING IN THE CENTRAL AND SOUTHERN
WILLAMETTE VALLEY AFTER 15Z MON UP TO 10 KTS WITH GUSTS UP TO
15-18 KT, DECREASING AFTER 03Z TUE.
KPDX AND APPROACHES...VFR CONDITIONS THROUGH THE TAF PERIOD EXCEPT
FOR A 40-50% CHANCE OF LOW STRATUS DEVELOPMENT SOMETIME BETWEEN
10-18Z MON. IF STRATUS DEVELOPS, EXPECT CONDITIONS TO FLUCTUATE
BETWEEN MVFR AND IFR. NORTH TO NORTHWEST WINDS LESS THAN 5 KTS,
INCREASING TO 6-8 KTS AFTER 18Z MON. -HEC
MARINE
NORTHWESTERLY WINDS, INCREASING TO AROUND 10-15 MPH
WITH GUSTS UP TO 20 KT THIS AFTERNOON AND EVENING, MAINLY FOR
ZONES PZZ272, 273, 252, AND 253. THERE COULD BE SOME ISOLATED
GUSTS UP TO 25 KT FOR THOSE ZONES AS WELL, BUT NOT WIDESPREAD
ENOUGH FOR A SMALL CRAFT ADVISORY AT THIS TIME. WILL MONITOR
OBSERVATIONS IN CASE THIS CHANGES. SEAS 4-6 FEET AT 10-12 SECONDS
EXPECTED THROUGH THE MIDDLE OF THE WEEK AS A NORTHWESTERLY SWELL
MOVES INTO THE WATERS.
WEAK OFFSHORE FLOW WILL DEVELOP BRIEFLY LATE TONIGHT INTO TUESDAY
MORNING. HOWEVER, THIS WILL BE SHORT LIVED AS ANOTHER LOW
PRESSURE SYSTEM AND ASSOCIATED SURFACE FRONT APPROACHES THE WATERS
TUESDAY INTO WEDNESDAY. AS THE SYSTEM APPROACHES, WINDS BECOME
WEST/NORTHWEST AND WILL INCREASE WITH GUSTS UP TO 25 KTS. SEAS
WILL ALSO BUILD TOWARDS 7-10 FT, AS WELL. THERE STILL REMAINS
SOME UNCERTAINTY AS TO THE EXACT TIMING AND OVERALL STRENGTH OF
THE MIDWEEK SYSTEM, SO WILL HOLD OFF ON ISSUING ANY SMALL CRAFT
ADVISORIES AT THIS TIME. -HEC
PQR WATCHES/WARNINGS/ADVISORIES
OR...NONE.
WA...NONE.
PZ...NONE.
WWW.WEATHER.GOV/PORTLAND
INTERACT WITH US VIA SOCIAL MEDIA:
WWW.FACEBOOK.COM/NWSPORTLAND
X.COM/NWSPORTLAND
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page